In recent years, as display methods for liquid crystal display devices, wide viewing angle modes such as the MVA (Multidomain Vertical Alignment) mode and the IPS (In-Plain Switching) mode have been proposed. Among others, due to being a vertical alignment mode, the MVA mode is characterized by a higher contrast ratio than that of the IPS mode, and is widely used for applications such as TV sets.
In an MVA-type liquid crystal display device, on the liquid crystal layer sides of a pair of substrates opposing each other with a vertical-alignment type liquid crystal layer interposed therebetween, alignment regulating structures (also referred to as domain regulating structures) are provided so as to form a plurality of liquid crystal domains whose directors are in different alignment directions (directions of tilt). As the alignment regulating structures, apertures (slits) provided in the electrodes or dielectric protrusions (ribs) formed on the liquid crystal layer side of the electrodes are used (Patent Document 1).
Typically, on each of the pair of substrates, alignment regulating structures in straight-line form extending in two directions that are orthogonal to each other (hereinafter referred to as “linear alignment regulating structures”) are provided, such that, when viewed from a direction which is perpendicular to the substrates, the linear alignment regulating structures formed on one substrate and the linear alignment regulating structures provided on the other substrate appear parallel and alternating. As a result, when a voltage is applied across the liquid crystal layer in an arbitrary pixel, four domains are created in between the linear alignment regulating structures, whose liquid crystal molecules would fall in azimuths (also called the azimuths of liquid crystal domain directors) which are mutually apart by about 90°. Typically, four liquid crystal domains are created the azimuth angles of whose liquid crystal domain directors constitute 45° with respect to the polarization axes (transmission axes) of a pair of polarizers which are placed in crossed Nicols. When an azimuth angle of 0° is the direction of the polarization axis of one polarizer (e.g., the horizontal direction on the display surface) and positive azimuths are defined in the counterclockwise direction, the azimuth angles of the directors of the four liquid crystal domains are 45°, 135°, 225°, and 315°.
Note that a “pixel” in the present specification refers to the smallest unit by which a liquid crystal display device performs displaying, and in the case of a color display device, refers to the smallest unit that displays each individual primary color (typically R, G, or B), occasionally referred to as a “dot”.
As described above, in a typical MVA-type liquid crystal display device, the linear alignment regulating structures extend at an angle of 45° with respect to the horizontal direction (and the vertical direction). On the other hand, a typical pixel electrode has an edge extending along the horizontal direction or the vertical direction, and an oblique electric field (fringe field) is generated also near the edge of the pixel electrode. Therefore, near the edge of the pixel electrode, liquid crystal molecules may be aligned in a direction which is different from the direction of alignment regulation by the linear alignment regulating structures, whereby a schlieren texture may be formed. When liquid crystal molecules are aligned in a direction which is different from the direction of alignment regulation by the linear alignment regulating structures in this manner, the display quality (particularly luminance) is deteriorated.
According to Patent Document 1, an improvement in display quality is possible by providing auxiliary alignment regulating structures close to the portion near the edge of the pixel electrode where a schlieren texture is observed. The auxiliary alignment regulating structures are formed so as to be integral with the linear alignment regulating structures which are provided on the counter electrode (i.e., on the liquid crystal layer side of the counter electrode). Due to an alignment regulating force from the auxiliary alignment regulating structures, the alignment of the liquid crystal molecules near the edge of the pixel electrode matches the alignment of the liquid crystal molecules in the central portion of the pixel, so that no schlieren texture is formed and the display quality is improved. The entire disclosure of Patent Document 1 is incorporated herein by reference.